The present invention relates to a fuel injection control system for internal combustion engines, and more particularly to an electronic fuel injection control device for electrically controlling an amount of fuel supply into an internal combustion engine from a source of fuel in automotive vehicles.
In conventional electronic fuel injection control devices, physical values such as an amount of suction air, an intake manifold negative pressure in operation of an internal combustion engine are calculated, in general, to determine an amount of fuel supply into the engine from a source of fuel. However, such physical values pulsate due to reverse flow of combustion gases into the intake manifold synchronously caused at a frequency of explosion of air-fuel mixture in the combustion chamber. It has been, therefore, observed that the amount of fuel supply or the ratio of air-fuel fluctuates due to such pulsation of the physical values, resulting in disorder of rotational speed or output power of the engine. In order to overcome such problems, a Japanese Patent Early Publication No. 57-2433 discloses a fuel injection control system which is arranged to determine an amount of fuel supply in dependence upon an average amount of the air sucked into respective cylinder barrels of the engine during one rotation in its normal operation and further in dependence upon an amount of the air sucked into one of the cylinder barrels of the engine at a termination of one rotation in its transient operation for quick acceleration of the vehicle. In this type of fuel injection control system, a high speed analogue-to-digital converter such as a converter of the progressive conversion type is utilized to convert an analogue voltage representing the amount of suction air to a digital value at an extremely high speed e.g. several hundreds microseconds. During such high speed conversion of the analogue voltage, high frequency noises are converted together with the analogue voltage to cause an error in the digital value. As a result, there will occur an error in determination of the amount of fuel supply particularly based on a single digital value corresponding with the amount of suction air at the termination of one rotation of the engine.